WordNet (r) 3.0 (2006):

in operation
    adj 1: being in effect or operation; "de facto apartheid is
           still operational even in the `new' African nations"-
           Leslie Marmon Silko; "bus service is in operation during
           the emergency"; "the company had several operating
           divisions" [syn: operational, in operation(p),
           operating(a)]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "in operation":
   acting, active, at work, functional, functioning, going, going on,
   in commission, in effect, in exercise, in force, in hand, in play,
   in practice, in process, in service, in the works, in use,
   inaction, on foot, on the fire, ongoing, operating, operational,
   running, working